as soon as the booting process has been finished ,the monitor doesn't display my desktop but it shows some colors.when i turn it off and switch it on again
then it works normally.this happens every time.help me in overcoming this problem.

Did it ever work OK?

If so do you remember anything happening when it started to fail?

New hardware and or software?

Sounds like the initial boot is not activating the graphics card.

Many high end cards have their own BIOS which might be tripping over the motherboard BIOS.

I would swap monitors with another PC and see if the problem follows the monitor, or stays with the PC.